While discussing the options of a cold roof to avoid potential problems with ice damming with an architect, he felt that snow load, that is to say snow over the top of a continuous ridge vent would render the concept invalid. The location is in the snow belt of Cleveland Ohio area where we can get up to 10 inches of snow per storm. This is on a retrofit for a 140 year old home with little or no existing insulation. The current specs are for max insulation on existing roof (both under deck if accessible and over decking foam board as well as sprayed foam (assume best effort to avoid air leakage) and a 1.5 to 2 inch air space between second deck and insulated deck. These dimensions were chosen to produce an esthetically acceptable soffit and edge of roof detail. Any thoughts?
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Snow doesn't seem to cause problems for ridge vents here (southern MN), though we don't get as much snow as Cleveland.
And if the snow causes problems for ridge vents, it'll cause problems for conventional vents.
A cold roof is fully vented by definition. Seems like your archie is unfamilar with the concept
A cold roof is fully vented by definition. Seems like your archie is unfamilar with the concept
WTF?!>?!>!
I had to do a verification thing four fricken times before my reply posted
Paul
It probably doesn't like your "whole gang" thing.
You know, sort of like everything you read here ain't worth a shit.
Community college vs. Yale.
I asked a similar question some time ago
I got teh same kind of non-answers. No offense to anyone, but no one seems to know anything about the subject. They do know that they build ridge vents in areas where they are covered with deep dnow. And that, that is the way it is done. Not much help.
I can not argue with the fact that, that is the way it is done. And I suppose with reasonable results as no one is throwing the concept out and building hot roofs, which must be what your archy is pushing for.
It seems to me that neither method is perfect in cases where deep snow collects on the roof. My thinking is that in both cases some heat does more through the insulation. It has too or else you could heat your house one time and the heat would stay there all winter. WE know this is not teh case so some heat is moving through the insulation and of course through air leaks. In either case teh heat gets to the roof. In the hot roof method this heat must melt some of the snow, hopefully al be it slowly. But that is a risk of ice damns at teh eaves. In the cold roof method the theory is the warm air getting through the insulation exits at the ridge before it melts any snow! However, I like your archy ask and did ask, does the warm air get stopped at teh ridge by the snow? IF so it too will melt snow.
Of course snow is permeable and therefore, perhaps the warm air works up through the snow and escaping before melting much snow. If this is true a cold roof would be superior to the hot roof.
Just my thoughts which are as good as " that is the way we build them". LOL.
Sounds like you are not familiar with what a cold roof platform is either, Doright.
What makes yiou think he got a non-answer?
Are usual I have forgotten more about cold roofs than you every will know as your "non-answer" shows. As for other answers in this thread which you insist are there, other than "that is the way they do it so they must work", point to one, please.
As I said in my first post, "no offense" but no one seems to know anything about this subject. Please, by all means, answer the question. The point is no one here including yourself( no surprise) has explained how, or if, or proven THAT WARM AIR GETTING TO THE VENT SPACE IS CAPABLE OF ADEQUATELY TRAVELING THROUGH SEVERAL INCHES LET ALONE SEVEAL FEET OF SNOW ONCE IT GETS TO THE RIDGE VENT. For anyone capable of reading (hmm?) this is obviously the archy's point or concern.
I don't expect an anwser from you of course, but some one out there must have some knowledge.
One web site http://www.guttercap.com states "Occasionly the roof vents will become covered with an insulating layer of snow. The trapped air will then melt the snow at a faster pace."
Just one article to support your archy. Of course there are other ways to vent cold roofs. Perhaps Piffin could expalin it to you. LOL LOL!!!!!!
Do right
It's apparent that you are seemingly directing all your efforts to get the warm air out of the atiic space. I contend that if you spent that energy on keeping the warm air from escaping through the envelope and into the attic, you'd not have to worry about evacuating the little bit that does make it in there.
You portray the reason for a vented roof is to eliminate the end result of ice damming. However, there is a spring/summer/fall reason also-to cool the attic space thus prolonging shingle life and the comfort of the area below that attic, thus saving energy trying to cool it.
Whole lotta warm air escaping into the attic-whole lotta ventilation needed to remove it. None or not much getting in there, way less need for venting in the winter months.
There's probably some science behind this, but I think these ideas slide into the relm of common sense.
This from a dumb carpenter.
Of course there are reasons to cool a shingled roof in teh hot season, but the threads original questin had to do with "what happens when the ridge vent is covered in snow". Therefore the focus. I try to stay on topic. Perhaps you need to reread the post.
As for my concern with evacuating warm air from under the roof, it appears you continue to deny the obvious that no matter how well you air seal or insulate for that matter, HEAT WILL TRANSFER THROUGH THE INSULATION thus heating the vent space or roof deck, PERIOD. Again no matter how well you seal it.!!! IF this were not true and you had perfect sealing you would be able to heat your house once in December and never heat it again as you seem to imply that NO HEAT IS LOST throught hte roof. Just ain't gonna ever happen. SO the question is "what to do about that heat". NOW the answer may be that the amount is so low as to melt an immaterial amount of snow, but I have not seen any information regarding that.
damn it doright
NOW the answer may be that the amount is so low as to melt an immaterial amount of snow, but I have not seen any information regarding that.
What do you want for information? Build it proper and it'll be minimal leakage, and minimal problem. So minimal it'll be no problem.
Sure, live in the alps or other extremes or locations and you build to that. LOCAL VARIATION.
There is no set WAY that works universal.
Is that on topic?
No reason to get your undies in a bundie. YOu must admit your posts can be a bit abrasive, ie suggesting I have said something which I never did. And actually reading a post can be helpful.
The point is that you say "build it proper". Well what is proper? You seem to relie on proper being "the way we / you always build it". There is no doubt "they build them with ridge vents", and that can be the end of the story. Or we can have ACTUAL INFORMATION on whether warm air moves through snow and if so how much and how fast. That would be information.
It appears your experience in your climate is that ridge vents either never get buried in snow or teh system seems to just plain work. In that case I can see why you get testy. But perhpas you can put yourself in a place where you can relate to situations where you do get four feet of snow on a roof with periods of freeze and thaw. You don't have INFORMATION in that case, no fowl there no harm there just a fact.
I KNOW I have can vents , full soffit vents in a pretty well insulated house currently. When I get two feet of snow on the roof that completely covers the vents and the rigth temperature conditions occur I get ice damns on the north side. If the vents are not covered (ie they melt clear of a foot or so of snow) I never get damns. This seem to prove that air does not transfer well through the snow. It is also possible that if the house were better sealed no damns would form even though the vents do not function. (That is your position)
INFORMATION on the air permiblity of snow would be useful INFORMATION. I don't have it, you don't have it. Salave (spelling)
Be in good health.
Doright
Go to the Building Science website and absorb all the information there on the subject.
Build using their best practice.
I've had some experience with the 'cold roof,' though from the 'consumer' side. Let me walk us through what I had, and how it worked.
Newly built home, a roof/ceiling made of pre-fab panels that included 4" of foam. Add summer sun, and it was hot as hades. Then we built a framework over the existing roof, and did another 'roof' of clay tiles.
With the eaves wide open and the ridge vented, there was plenty of free air flow between the two roofs. This had the effect of placing the entire roof 'in the shade.' The difference in indoor comfort was incfredible.
Now you're asking about the other half of the year - when it is the cold you worry about.
As I see it, your attic itself ought not have a ridge vent - though gable vents might still be prudent. Instead, the ridge of the cold roof will be open, and vent the space between the layers. So what hapens in a heavy snowfall?
I expect that there will still be enough heat leakage and natural convection that the open ridge will blow itself clear of snow in all but the heaviest snowfalls. Even should the ridge become blocked, all the snow and ice will be on the cold roof - and not the actual roof. I can't see how an ice dam can form, or how water could back up and cause a leak.
That's an important point ... that the waterproofing is provided by the 'under' roof, and not the outer 'cold' roof. Roofing penetrations need to be sealed at the lower deck as well. Conceivably, the 'cold roof' could be made of shade screen and still be effective.
One detail to watch is that the cold roof needs to extend past the inner roof far enough that snow and ice will not block the 'intake' openings. Likewise, do not block them with rain gutters either.
I 've had some experience
Do you live in a climate cold enough to accumulate snow? If so I you have had sufficient snow to cover the Open ridege did yo ever get icicles? Ice damming at the roof edges? If not your reply has convinced me to tell teh architect it is my money, my risk of falling (who else clears the ice?) etc ... install it thank you !
oldhouse
I'm over in NW Ohio. Lived from age 5-18 in Solon. Since '67 till now, here.
I've lived in all sorts of construction with all sorts of heating and insulation configurations. I have never had damage causing ice dams. Luck on my part more than likely.
For the past 23 years we've lived in what I built. 2-story, built into the hill on the north side. In the woods, no gutters. We get some icicles on the east side of the hip roof (there's a 2'x4' skylight there). 2'-overhang, no leakage into the soffits. Ice and water at the hip eaves below arch shingles.
Mushroom roof vents mainly on the south and north, 15' of ridge vent. Sure, snow sits on the roof, covers the ridge and vents. None blows in.
We do not get the volume of the snow belt or just west of Rt. 91. Probably not much help, but at least I'm in the same lattitude (?)......................or is it longitude.
Go Tribe!
" "Hot" and "cold" roof
"
"Hot" and "cold" roof design and construction can get complex and can made it difficult to assign proper terminology to each. Regional variations also muddy the waters - I would expect things to be a little different in Alaska! But let's look at the roofs in their simplest forms:
A "hot" roof simply means that heat (and humidity) from the conditioned space below can get into the attic/air space above the insulation (there must be some degree of attic/air space above the insulation). This warmer air can cause snow/ice to melt on the roof surface above, which then refreezes on the unheated overhang, leading to ice-damming. The air cavities take on heat; that's the origination of the term "hot roof" and the reason why the cold roof method was invented.
A "cold" roof is "sealed tight"; there's no attic/air space for heat to leak in to, so the building materials remain "cold". Hence the term.
That's the basics. A cold roof is further defined (when properly designed and built) by a second layer of plywood, over sleepers, creating an airspace that keeps the slightly-warmer building materials below from making any contact with snow or ice. That may be the source of confusion - there IS an airspace in a proper cold roof, but it's not above the insulation; it's OUTSIDE of the primary roof.
I would refer you to page 288 of the JLC Field Guide to Residential Construction and page 192 of Rob Thallon's Graphic Guide to Frame Construction. This is information straight from the field (my preferred source).
from: http://en.allexperts.com/q/Architecture-2369/Hot-Cold-Roof.htm
I am amazed at how much bad terminology and mis-use of the term there is out there re cold roofs
Not a terribly bad article here:
http://www.google.com/imgres?imgurl=https://www.finehomebuilding.com/CMS/uploadedImages/Images/Homebuilding/Articles/021063042_sprd.jpg&imgrefurl=https://www.finehomebuilding.com/how-to/articles/framing-roofs-to-prevent-ice-damming.aspx%3Fac%3Dfp&usg=__YYWjTXkE6ntqnpf4TtbgWn2YYOk=&h=275&w=408&sz=42&hl=en&start=5&sig2=QuGmnR3-9H1Txdp2XaCAFw&zoom=1&tbnid=oW7420tbsrahWM:&tbnh=84&tbnw=125&ei=ZLGrTZKvF4Oa0QGc5d35CA&prev=/search%3Fq%3Dcold%2Broof%26hl%3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official%26biw%3D1005%26bih%3D541%26tbm%3Disch&itbs=1
I think some of the mis-understanding comes from taking the noun "Coldroof" and separating it to be an adjective Cold and a noun Roof. Both share the same goal, bu ta cold roof ( noun) is a distinctive method fpor framing that totally separates two distinct roof planes so that no warm air from inside ever gains access to the cold portion so it never needs to be vented out through a ridge vent
Basics to build a coldroof:, you frame normally for structure, and sheathe it, apply the underlayment ( tarpaper or syntheic such as Titanium UDL or RTGII) then add 2x4 or 2x2 furring and a second sheathing layer to which is applied the shingles, metal, membrane or whatever.
There are modifications of this, such as when slates or tiles are installed suspended off the deck on the 2x2s.
A vented attic space aims at the same gaol, but generally performs less efficiently than a true coldroof. It is a shame the terminoloigy gets mixed and mingled.
Same thing on the other side - there are 2-3 diofferent kinds and meanings of a hot roof, depending on context
A "hot" roof simply means
A "hot" roof simply means that heat (and humidity) from the conditioned space below can get into the attic/air space above the insulation (there must be some degree of attic/air space above the insulation). This warmer air can cause snow/ice to melt on the roof surface above, which then refreezes on the unheated overhang, leading to ice-damming. The air cavities take on heat; that's the origination of the term "hot roof" and the reason why the cold roof method was invented.
That seems to contradict the first web page you referenced.
I always took "hot roof" to mean a roof that has the insulation directly below the roof surface -- hence the roof would supposedly get "hot" in the sun, because there was no ventilation. A "cold roof", by this definition, has the insulation farther below the roof surface, with ventilation of some sort in-between. Your web reference seems to agree with me.
A "cold roof" is the conventional peaked roof design with insulation between living space and "attic". A "hot roof" is more likely to be a flat roof or a cathedral roof.
The terms concern the environment the roofing (supposedly) faces, with the "hot" roof being harder on the roofing. At one point roofing manufacturers were (supposedly) not warranting shingles installed on "hot" roofs.
Note that these definitions have little to do with the ice dam issue. In a lot of ways a "hot" roof is apt to be better from an ice dam standpoint, because it's easier to get a good continuous insulation layer by, eg, covering the roof sheating with foamboard.
DanH, I am with you. I have never heard anything like what Piffin describes as a hot roof. I have typiclaly heard of it being done with spray foam directly to the underside of the roof shealthing, hence the deck gets hot becuase it can not shed the heat up through the ridge vent. Piffin seems confused. He described a cold roof and labeled it cold. He was right in that a "proper" cold roof has a second over lay on top of the main roof deck, but to say that a conventionally roofed roof with a space between teh insulation and the shealthing is a hot roof is just plain wrong.
Your architect's concern may be valid, given that snow is a very changeable material as regards its air-permeabilty.
I would guess that Cleveland gets a lot of wet snow that can partially thaw and then re-freeze, resulting in a nearly air tight layer thru much of the winter.
If that happens, and the roof vents for either or both airspaces were defeated, there could be a resulting buildup of attic heat.